Three-dimensional diagnostic images of the brain, spinal cord, and other body portions can be produced by diagnostic imaging equipment such as CT scanners, magnetic resonance imagers, three-dimensional fluoroscopes, and the like. These imaging modalities often provide structural detail with a resolution of a millimeter or better. Image guided interventional systems have been developed to utilize this data to assist a doctor, surgeon or other specialist in connection with planning of an medical, surgical or other type of interventional procedure and in accurately locating a region of interest within the body of a patient during the procedure.
Image guided interventional systems may also be used to display position and orientation of a medical tool with respect to the images of the patient during a interventional procedure. Multiple views of patient image data are typically displayed on a monitor visible to the person handling the tool during a medical or medical procedure. These views may include axial, sagittal, and coronal views of the patient. A fourth oblique view is sometimes displayed, presenting image data in a plane orthogonal to a tip of the tool. The location of the tip of the tool, the tool's trajectory, and diameter of the tool head are displayed on one or more of these images. The algebraic distance between the tip of the tool and a desired position may also be displayed numerically on the monitor.
Given the nature of image guided procedures, it is necessary to be able to track the location of the tip of the tool, the tool's trajectory, and diameter of the tool head with a high degree of precision, often requiring calibration to less than a millimeter in accuracy. The position and orientation of tools are tracked by use of a tracking system. The tracking system tracks the tools by detecting the position of three or more markers that have a known geometric relationship with respect to each other and to the tool. The tracking system may utilize any type of tracking technique, for example optical, magnetic, radio frequency, and fiber-optic, to name a few. The markers can be, depending on the type of system, passive or active. One well known example of a tracking system uses as markers spheres that reflect infrared energy. The tracking systems baths the spheres in infrared radiation. Multiple, spatially separated cameras are used detect the relative positions of the spheres.
The position indicating elements, or markers, are positioned in a unique pattern for each tool in order to allow the tracking system to be able to distinguish one tool from another. In other words, the unique pattern can be said to characterize the tool. The tracking system is preprogrammed with information related to where the tip and trajectory of each tool is with respect to the tool's position indicating elements and with information related to the diameter of the tool head. For instance, with respect to a tracked probe having three infrared emitters, the tracking system maintains information related to where the tip of the probe is with relationship to a selected point on a plane defined by the three infrared emitters. Based on this information, a precise location of the tip can be calculated and displayed on one of the monitors.
In a variety of medical tools such as drills, probes, endoscopes, etc., it is often beneficial to a doctor, surgeon or other individual to make changes to the tool which may affect the positioning of the tip as well as the diameter of the tool head. For instance, on a medical drill it is often helpful for the surgeon to be able to change the size and length of a drill bit to perform different medical procedures. Further, with respect to the probes, it is often desirous to replace different length and diameter shafts on the probe handle in order to reach different regions in the patient.
Unfortunately, because the position of the tip of each tool with respect to the tool's position indicating elements and the tool head diameter in conventional systems are preprogrammed changes to the tool which affect the location of the tip and diameter of the tool head cannot easily be made. If changes are made, an operator needs to measure the new relationship between the tip of the tool and the tool's position indicating elements and enter this information into the computer. Further, information related to a new diameter of the tool head may also need to be entered. This process is time consuming and cumbersome. If the new information is not entered into the tracking system, the tip of the tool will not be properly tracked and displayed on the monitor.
It is desirable to allow standard surgery tools to be used with image guided intervention systems. This feature would help to keep down the cost of image guided surgeries. Such a tool calibrator is disclosed in U.S. Pat. No. 5,987,960, which is incorporated herein by reference. The tool calibrator includes two movable blocks shaped to slidably engage and secure a tool in a desired position. The tool is secured by a series of staggered V shaped grooves on each of the two movable blocks having a known geometrical relationship with a diameter of a tool head of the tool. The tool calibrator further includes at least one position indicating element for communicating a location of the tool calibrator in an operating room or other area. A position and direction of a tip of the tool is determined by comparing a location of the tool secured within the tool calibrator to the location of each of the two movably blocks. Further, based on the location of each of the two movable blocks, the diameter of the tool head is calculated. The tool calibrator is able to calibrate a location of a tip of a tool, a direction in which the tip is pointing, and a diameter of a tool head all at once. The direction in which the tip of the tool is pointing is determined by comparing a relationship between position indicating elements connected to each of the two movable blocks securing the tool with position indicating elements connected to the tool. The location of the tip of the tool is determined by comparing the location of the position indicating elements connected to the tool calibrator to the location of position indicating elements connected to the tool. The diameter of the tool is determined by virtue of a known geometrical relationship between the V shaped grooves of two movable blocks and the diameter of the tool head.